Most popular music follows a common structure with sections like introductions, verses, choruses, and bridges that are typically divided into phrases of 4, 8, or 16 bars. These sections contrast melodically and through other musical elements to maintain interest. While most songs change harmony between verses and choruses, some like "Stand By Me" use the same harmony. Structure can also be delineated through polyrhythms, as in "Kashmir" by Led Zeppelin, or variations in meter.